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<html lang="en">
<head>
    <meta charset="UTF-8">
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    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
<script>
    //全局作用域
    var num = 20;            //全局变量
    function fun(){
        //局部作用域
        var num = 10;        //局部变量
        console.log(num);    //输出局部变量值
    }
    fun();
    console.log(num);        //输出全局变量值
</script>
</body>
</html>